OK, if we are going to be picky here, lets take the example of the replacement socket. Customer has rang and said it has got whacked and is all broken, can you come and have a look. It is on the way to a decent rewire you have on the go. So you call in, hoping for a bit of pie and mash (hope that doesn't start another debate) and a sharp exit. Socket is in bits, so swap it, do a quick Zs, everything is good. Now, really, what you should do is an RFC test at the CU to make sure there is still continuity, and then maybe all the other stuff like IR and RCD if present. But hang on, you need to do the RFC test first just in case it is broken anyway, before you start, else if it is broken after have you done it was it like it anyway? No time for a cuppa and so on, just sorted a potentially dangerous situation out and got a bit of beer money, everyone is happy including the customer. Now, in these circumstances, are we going to disconnect the circuit and do said tests? Or are we going to move on leaving the situation better than before, and crack on with our rewire? Or maybe refuse to change it at all if the RFC is not continuous? We could spend another 20 mins discussing the virtues of RCD protection and periodic testing and bringing the bonding up to spec, but 99/100 customers will just watch us driving away shaking their head, thinking "just like plumbers that lot....." And THEN we have to write out a MWC cert and drop it off another time unless you have a portable printer in the van, cos Mrs Jones does not have email. It's not easy, being cheesy.